Conventionally in the motor used for starters, the space factor of the field coil in the motor was increased as an effective method to downsize the motor.
In this case, a straight planar conductor covered with an insulation film having a sufficient insulation resistance has been used generally. If this straight planar conductor is applied to a field device having four magnetic poles as shown in FIG. 6, the straight planar conductor 20 is wound around a pole core 4 of a stator 3 as shown in FIG. 5, one end 20a of the straight planar conductor 20 is connected to the straight planar conductor wound on the neighboring magnetic pole via a connector bar 8, and the other end 20b is connected to a brush 5.
In the abovementioned conventional straight planar conductor 20, the straight planar conductor is wound on the pole core 4, so the insulation films on the surfaces of the straight planar conductors 20 contact creating a double layer insulation films. This causes the need to wind wire to form the field coil. Further, although the withstanding voltage between the straight planar conductors is lower than between the stator 3 and the straight planar conductor 20, the insulation films become excessive between the straight planar conductors. Thus, the problem of a decrease in the space factor of the field coil occurs.
This invention overcomes the above problems, and provides a field coil that can greatly increase the space factor without requiring winding on a pole core.